Indian Ocean winds: changes and challenges
Lean, Katie ; Bormann, Niels
On 2 March 2017, the geostationary satellite Meteosat-8 became the operational Indian Ocean Data Coverage (IODC) service in the ECMWF data assimilation system. With effect from that date, Atmospheric Motion Vectors (AMVs) and All Sky Radiances (ASRs) from the second-generation Meteosat-8 replaced the equivalent products from the retiring, first-generation Meteosat-7 satellite. AMVs and ASRs provide important information about wind and water vapour, respectively. Experiments have shown that assimilating the new data brings increased benefits compared to using Meteosat-7. However, they have also uncovered an area confined to the centre of the Indian Ocean at lower heights (around 850 hPa) where the benefit of the AMVs is less clear, due to a combination of model biases, suspected height assignment problems and difficulties in forecast verification.
<br>A subsequent, more in-depth investigation of Indian Ocean AMVs considered other satellites providing good coverage. Meteosat-8 was compared with Indian National Satellite - 3D (INSAT-3D) and China's Feng-Yun - 2E (FY-2E) to consider their relative benefits or limitations. Despite different data quality characteristics, the impacts on the forecast from the different satellites were surprisingly consistent. This work also presented an opportunity to look more closely at the problematic low-level area over the ocean. The situation was revealed to be complicated with challenges for the model but also suspicious behaviour in the AMVs, in particular potentially too little variation of wind speed with height. Height assignment is a topic of great interest in the AMV community and the work presented here motivates a wider investigation and collaboration with AMV producers and other data users.
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